1,093 research outputs found
Gluon contribution to the dark matter direct detection
In this article we have calculated the spin-independent cross section of
nucleon-dark matter scattering process at loop level, which is relevant to dark
matter direct detection. Paying particular attention to the scattering of gluon
with dark matter, which contributes as leading order in the perturbation, we
have systematically evaluated loop diagrams with tracking the characteristic
loop momentum which dominates in the loops. Here loop diagrams whose typical
loop momentum scales are the masses of quarks and other heavier particles are
separately presented. Then, we have properly taken into account each
contribution to give the cross section. We assume that the dark matter is pure
bino or wino in the supersymmetric models. The application to other models is
straightforward.Comment: 23 pages, 10 figure
Electrons doped in cubic perovskite SrMnO3: isotropic metal versus chainlike ordering of Jahn-Teller polarons
Single crystals of electron-doped SrMnO3 with a cubic perovskite structure
have been systematically investigated as the most canonical
(orbital-degenerate) double-exchange system, whose ground states have been
still theoretically controversial. With only 1-2% electron doping by Ce
substitution for Sr, a G-type antiferromagnetic metal with a tiny spin canting
in a cubic lattice shows up as the ground state, where the Jahn-Teller polarons
with heavy mass are likely to form. Further electron doping above 4%, however,
replaces this isotropic metal with an insulator with tetragonal lattice
distortion, accompanied by a quasi-one-dimensional 3z^2-r^2 orbital ordering
with the C-type antiferromagnetism. The self-organization of such dilute
polarons may reflect the critical role of the cooperative Jahn-Teller effect
that is most effective in the originally cubic system.Comment: 5 pages, 4 figure
Room-temperature ferromagnetism in Sr_(1-x)Y_xCoO_(3-delta) (0.2 < x < 0.25)
We have measured magnetic susceptibility and resistivity of
SrYCoO ( 0.1, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3,
and 0.4), and have found that SrYCoO is a room
temperature ferromagnet with a Curie temperature of 335 K in a narrow
compositional range of 0.2 0.25. This is the highest transition
temperature among perovskite Co oxides. The saturation magnetization for
0.225 is 0.25 /Co at 10 K, which implies that the observed
ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar
Sr/Y ordering.Comment: 5 pages, 4 figure
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